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Cheap Flights from St Louis (STL) to Ontario (ONT)

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      Travellers and cabin class, 1 Adult, Economy

      Compare St Louis to Ontario International flight deals

      Find the cheapest month or even day of the year to fly to Ontario International

      Book the best Ontario International fare with no extra fees

      Flight deals from St Louis to Ontario International

      Looking for a cheap last-minute deal or the best return flight from St Louis Airport to Ontario International Airport? If you want to travel next month, return fares start from $252. Find the lowest prices on one-way and return tickets right here.
      Ontario.$252 per passenger.Departing Sat, 12 Sep, returning Sat, 19 Sep.Return flight with Frontier Airlines.Outbound indirect flight with Frontier Airlines, departs from St Louis on Sat, 12 Sep, arriving in Ontario International.Inbound indirect flight with Frontier Airlines, departs from Ontario International on Sat, 19 Sep, arriving in St Louis.Price includes taxes and charges.From $252, select.
      Ontario.$376 per passenger.Departing Sat, 10 Oct, returning Fri, 16 Oct.Return flight with Frontier Airlines.Outbound indirect flight with Frontier Airlines, departs from St Louis on Sat, 10 Oct, arriving in Ontario International.Inbound indirect flight with Frontier Airlines, departs from Ontario International on Fri, 16 Oct, arriving in St Louis.Price includes taxes and charges.From $376, select.
      Ontario.$378 per passenger.Departing Wed, 30 Sep, returning Wed, 7 Oct.Return flight with Frontier Airlines.Outbound indirect flight with Frontier Airlines, departs from St Louis on Wed, 30 Sep, arriving in Ontario International.Inbound indirect flight with Frontier Airlines, departs from Ontario International on Wed, 7 Oct, arriving in St Louis.Price includes taxes and charges.From $378, select.
      Ontario.$379 per passenger.Departing Wed, 4 Nov, returning Thu, 5 Nov.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Wed, 4 Nov, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Thu, 5 Nov, arriving in St Louis.Price includes taxes and charges.From $379, select.
      Ontario.$487 per passenger.Departing Thu, 26 Nov, returning Wed, 2 Dec.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Thu, 26 Nov, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Wed, 2 Dec, arriving in St Louis.Price includes taxes and charges.From $487, select.
      Ontario.$498 per passenger.Departing Sat, 12 Dec, returning Tue, 15 Dec.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Sat, 12 Dec, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Tue, 15 Dec, arriving in St Louis.Price includes taxes and charges.From $498, select.
      Ontario.$501 per passenger.Departing Wed, 28 Oct, returning Mon, 2 Nov.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Wed, 28 Oct, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Mon, 2 Nov, arriving in St Louis.Price includes taxes and charges.From $501, select.
      Ontario.$505 per passenger.Departing Mon, 25 Jan, returning Fri, 29 Jan.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Mon, 25 Jan, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Fri, 29 Jan, arriving in St Louis.Price includes taxes and charges.From $505, select.
      Ontario.$520 per passenger.Departing Sun, 30 Aug, returning Thu, 3 Sep.Return flight with Frontier Airlines.Outbound indirect flight with Frontier Airlines, departs from St Louis on Sun, 30 Aug, arriving in Ontario International.Inbound indirect flight with Frontier Airlines, departs from Ontario International on Thu, 3 Sep, arriving in St Louis.Price includes taxes and charges.From $520, select.
      Ontario.$522 per passenger.Departing Fri, 28 Aug, returning Mon, 31 Aug.Return flight with Frontier Airlines.Outbound indirect flight with Frontier Airlines, departs from St Louis on Fri, 28 Aug, arriving in Ontario International.Inbound indirect flight with Frontier Airlines, departs from Ontario International on Mon, 31 Aug, arriving in St Louis.Price includes taxes and charges.From $522, select.
      Ontario.$558 per passenger.Departing Fri, 19 Feb, returning Mon, 22 Feb.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Fri, 19 Feb, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Mon, 22 Feb, arriving in St Louis.Price includes taxes and charges.From $558, select.
      Ontario.$584 per passenger.Departing Tue, 22 Dec, returning Fri, 8 Jan.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Tue, 22 Dec, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Fri, 8 Jan, arriving in St Louis.Price includes taxes and charges.From $584, select.
      Ontario.$596 per passenger.Departing Mon, 1 Mar, returning Mon, 8 Mar.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Mon, 1 Mar, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Mon, 8 Mar, arriving in St Louis.Price includes taxes and charges.From $596, select.
      Ontario.$631 per passenger.Departing Fri, 26 Feb, returning Mon, 8 Mar.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Fri, 26 Feb, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Mon, 8 Mar, arriving in St Louis.Price includes taxes and charges.From $631, select.
      Ontario.$666 per passenger.Departing Wed, 31 Mar, returning Mon, 5 Apr.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Wed, 31 Mar, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Mon, 5 Apr, arriving in St Louis.Price includes taxes and charges.From $666, select.
      Ontario.$713 per passenger.Departing Thu, 22 Oct, returning Thu, 21 Jan.Return flight with Southwest Airlines.Outbound indirect flight with Southwest Airlines, departs from St Louis on Thu, 22 Oct, arriving in Ontario International.Inbound indirect flight with Southwest Airlines, departs from Ontario International on Thu, 21 Jan, arriving in St Louis.Price includes taxes and charges.From $713, select.

      Find the cheapest month to fly from St Louis to Ontario International

      We’re always keeping an eye on fares, so you can find the best one in seconds. It looks like St Louis to Ontario International flights are currently cheapest in September.
      Aug
      from $522
      Sep
      from $252
      Oct
      from $376
      Nov
      from $379
      Dec
      from $498
      Jan
      from $505
      Feb
      from $558
      Mar
      from $596
      Apr
      Find prices
      May
      Find prices
      Jun
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      Jul
      Find prices

      St Louis to Ontario International: Alternative routes

      Compare routes from St Louis to Ontario below. You may find an airport to fly into that's cheaper, faster, or easier than Ontario International.

      Ontario International

      4km from central Ontario
      Closest
      from $252
      Search flights

      San Bernardino Norton AFB

      39km from central Ontario
      Search flights

      Santa Ana John Wayne

      48km from central Ontario
      from $318
      Search flights

      Long Beach Municipal

      54km from central Ontario
      from $388
      Search flights

      Hawthorne

      65km from central Ontario
      Search flights

      Burbank

      67km from central Ontario
      from $335
      Search flights

      Los Angeles International

      71km from central Ontario
      Cheapest
      from $218
      Search flights

      St Louis to Ontario: Flight information

      The things to know before you go.
      Cheapest flight found$252
      Cheapest month to flySeptember

      Finding cheap flights from St Louis to Ontario International: Frequently asked questions

      The best price we found for a return flight from St Louis to Ontario International is $252. This is an estimate based on information collected from different airlines and travel providers over the last 4 days and is subject to change and availability.
      Currently, there are no airlines that fly direct from St Louis to Ontario International. But we found flights with one or more stops from $252.
      As of August 2026, there are no flights flying from St Louis to Ontario International.
      The cheapest month to fly from St Louis to Ontario International is usually September.
      After crunching the numbers on our flight calendar, we found that it's currently cheapest to fly from St Louis Airport to Ontario International Airport on Saturday, 12 September 2026.
      No airlines currently offer direct flights between St Louis Airport and Ontario International Airport. Most routes have one or more stops.
      We show every price from over 1,200 airlines and travel agents, comparing them all so you don’t have to. If you know you want to fly to Ontario International but you’re not ready to book, set up a Price Alert. We’ll track prices for you, and let you know when they rise or fall.

      We crunched all the numbers in our flight calendar and it looks like the cheapest time to book a flight to Ontario is around 40 days in advance, so don’t leave your flight to the last minute.

      Currently, Frontier Airlines offers the cheapest flight tickets to Ontario International.

      Flying from St Louis Airport (STL) to Ontario International Airport (ONT): what you need to know

      • Ontario's timezone is UTC-8, making Ontario two hours behind St Louis.

      • Arrive at the airport on time so you don't miss your STL to ONT flight. Be there at least two hours ahead for international flights and an hour early for domestic departures to avoid a last-minute sprint to the gate.

      • Travelling during a peak month like July? Major public holidays and other high seasons can lead to longer lines at security. Play it safe and arrive up to four hours ahead of an international flight and two hours before domestic departures.

      • If you'd like to explore another city along the way, simply uncheck 'Direct flights only' when searching for your ticket from St Louis Airport to Ontario International Airport. These are the top stopovers between STL and ONT:

        • Dallas Fort Worth International Airport

        • Denver International Airport

        • Phoenix Sky Harbour Airport

      How to find the cheapest flights from St Louis Airport (STL) to Ontario International Airport (ONT)

      • $169 is the best price for a one-way St Louis Airport to Ontario International Airport flight. A return flight starts at $252. These fares may change depending on availability and demand.

      • It's usually best to book ahead of time if you're hoping to get cheap tickets from STL to ONT. That's because airlines adjust prices based on demand, which tends to rise closer to the date of departure.

      • The 'Whole month' tool shows you the cheapest flights from St Louis Airport to Ontario International Airport across the month. It's a great way to snap up a bargain if your dates aren't set in stone.

      • There's no need to check back in every day to see if fares have gone down when you set up a Price Alert. We'll notify you as soon as a special offer becomes available on cheap flights from STL to ONT.

      • Find the perfect flight for you with the help of the filters. To see the 'Fastest,' 'Cheapest' or 'Best' flights from St Louis Airport to Ontario International Airport, use the 'Sort by' tool. You can also filter results by arrival and departure times, airline, and journey duration.

      Handy information about St Louis Airport (STL)

      Arriving at Ontario International Airport (ONT)

      When to fly to Ontario International Airport (ONT)

      • July is the busiest month for flights from St Louis Airport to Ontario International Airport. To skip the crowds, go to Ontario in March.

      • The warmest month in Ontario is August, with temperatures ranging between 16ºC (61ºF) and 36ºC (97ºF). Book your flights from St Louis Airport to Ontario International Airport in this month if you like this kind of weather.

      • Look for cheap tickets from STL to ONT in February if you'd rather travel during cooler conditions. Temperatures are at their lowest then, ranging between 4ºC (39ºF) and 24ºC (75ºF) on average.

      Explore more of the United States

      • You've visited Ontario, now it's time to discover more of the United States. Journey around 56 kilometres west to Los Angeles to tick off its leading sights. From Hollywood Sign to Universal Studios Hollywood and Hollywood Bowl, you've got a jam-packed schedule ahead.

      • San Diego is another essential stop in the United States and is around 153 kilometres south of Ontario. No journey is complete without a visit to San Diego Zoo, San Diego Balboa Park and USS Midway Museum.

      Plan smart, explore more

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      Plan the rest of your trip from St Louis to Ontario

      Prices shown on this page are estimated lowest prices only. Found in the last 12 days.